Using linkage analysis and candidate gene screening, we have identified a total of five different genetic forms of congenital hyperinsulinism. (1) recessive mutations of the sulfonylurea receptor gene (SUR1), (2) recessive mutations of the potassium ion pore (Kir6.2), (3) dominant mutations of glucokinase (GK), (4) dominant mutations of glutamate dehydrogenase (GDH), (5) non-Mendelian expression of paternally-transmitted SUR1 mutations in focal hyperinsulinism. Studies are continuing to identify a third form of dominant hyperinsulinism and other forms of diazoxide-sensitive hyperinsulinism.